The search for new therapeutic agents has been greatly aided in recent years by better understanding of the structure of proteins and other biomolecules associated with target diseases. One important class of these proteins is the sigma receptor, a cell surface receptor of the central nervous system (CNS) which may be related to the dysphoric, hallucinogenic and cardiac stimulant effects of opioids. From studies of the biology and function of sigma receptors, evidence has been presented that sigma receptor ligands may be useful in the treatment of psychosis and movement disorders such as dystonia and tardive dyskinesia, and motor disturbances associated with Huntington's chorea or Tourette's syndrome and in Parkinson's disease (Walker, J. M. et al, Pharmacological Reviews, 1990, 42, 355). It has been reported that the known sigma receptor ligand rimcazole clinically shows effects in the treatment of psychosis (Snyder, S. H., Largent, B. L. J. Neuropsychiatry 1989, 1, 7). The sigma binding sites have preferential affinity for the dextrorotatory isomers of certain opiate benzomorphans, such as (+)SKF 10047, (+)cyclazocine, and (+)pentazocine and also for some narcoleptics such as haloperidol. The sigma receptor has at least two subtypes, which may be discriminated by stereoselective isomers of these pharmacoactive drugs. SKF 10047 has nanomolar affinity for the sigma-1 site, and has micromolar affinity for the sigma-2 site. Haloperidol has similar affinities for both subtypes. Endogenous sigma ligands are not known, although progesterone has been suggested to be one of them. Possible sigma-site-mediated drug effects include modulation of glutamate receptor function, neurotransmitter response, neuroprotection, behavior, and cognition (Quirion, R. et al. Trends Pharmacol. Sci., 1992, 13:85-86). Most studies have implied that sigma binding sites (receptors) are plasmalemmal elements of the signal transduction cascade. Drugs reported to be selective sigma ligands have been evaluated as antipsychotics (Hanner, M. et al. Proc. Natl. Acad Sci., 1996, 93:8072-8077). The existence of sigma receptors in the CNS, immune and endocrine systems have suggested a likelihood that it may serve as link between the three systems.
In view of the potential therapeutic applications of agonists or antagonists of the sigma receptor, a great effort has been directed to find selective ligands. Thus, the prior art discloses different sigma receptor ligands.
International Patent Application No. WO 91/09594 generically describes a broad class of sigma receptor ligands some of which are 4-phenylpiperidine, -tetrahydro-pyridine or -piperazine compounds having an optionally substituted aryl or heteroaryl, alkyl, alkenyl, alkynyl, alkoxy or alkoxyalkyl substituent on the ring N-atom. The terms aryl and heteroaryl are defined by mention of a number of such substituents.
European patent publication No. EP 0 414 289 A1 generically discloses a class of 1,2,3,4-tetrahydro-spiro[naphthalene-1,4′-piperidine] and 1,4-dihydro-spiro [naphthalene-1,4′-piperidine] derivatives substituted at the piperidine N-atom with a hydrocarbon group alleged to have selective sigma receptor antagonistic activity. The term hydrocarbon, as defined in said patent, covers all possible straight chained, cyclic, heterocyclic, etc. groups. However, only compounds having benzyl, phenethyl, cycloalkylmethyl, furyl- or thienylmethyl or lower alkyl or alkenyl as the hydrocarbon substituent at the piperidine nitrogen atom are specifically disclosed. The compounds are stated to displace tritiated di-tolyl guanidine (DTG) from sigma sites with potencies better than 200 nM. As a particularly preferred compound is mentioned 1-benzyl-1,2,3,4-tetrahydro-spiro[naphthalene-1,4′-piperidine].
European patent publication No. EP 0 445 974 A2 generically describes the corresponding spiro[indane-1,4′-piperidine] and spiro[benzocycloheptene-5,4′-piperidine] derivatives. Again the compounds are only stated to displace tritiated di-tolyl guanidine (DTG) from sigma sites with potencies better than 200 nM
European patent Application No. EP 0 431 943 A2 relates to a further extremely broad class of spiropiperidine compounds substituted at the piperidine N-atom and claimed to be useful as antiarrhythmics and for impaired cardiac pump function. The said application exemplifies several compounds, the majority of which contain an oxo and/or a sulfonylamino substituent in the spiro cyclic ring system. Of the remainder compounds, the main part has another polar substituent attached to the spiro nucleus and/or they have some polar substituents in the substituent on the piperidine N-atom. No suggestion or indication of effect of the compounds on the sigma receptor is given.
There is still a need to find compounds that have pharmacological activity towards the sigma receptor, being both effective and selective, and having good “drugability” properties, i.e. good pharmaceutical properties related to administration, distribution, metabolism and excretion.